I am an activist visiting NY in October. Have little time in NYC but would like to check out a (used) bookstore or two. Interested in philosophy, education, postcolonialism, Palestine and/or Edward Said, writers like Joseph Massad, Robert Jensen, Noam Chomsky, Sut Jhally, topics like (Jewish) anti-Zionism and generally speaking left wing, progressive ideas. Can you give me a name or two of (used) bookstores for someone with my interests?

In addition to Lia's suggestions - among them I am especially fond of Book Culture, where you will find a lot of discounted books relating to your areas of interest - I would also recommend the Strand and the Housing Works Bookstore/Cafe for used books. The former is a world-class and world-renowned institution, and the latter has the benefit of supporting a worthy cause.